The present invention relates to keyless systems for gaining entry into motor vehicles, and more particularly to passive remote keyless vehicle entry systems, which do not require activation by a user.
Automobiles traditionally have used mechanical keys and locks to protect against unauthorized access to the vehicle. However, mechanical locks are vulnerable to a criminal forcibly removing the lock cylinder, thereby being able to release the door catch without a key. Other vulnerability arises from the ability to duplicate easily most mechaincal keys.
With the increased use of electronic systems in vehicles came the ability to provide more sophisticated access control. Remote keyless entry (RKE) systems commonly take the form of a fob which is attached to the driver's key ring. The fob houses a radio transmitter which sends a digital code via a radio frequency (RF) signal to the vehicle when the driver presses a switch on the fob. The digital code prevents spurious radio signals from activating the door lock, as well as making it difficult for unauthorized persons to gain access to the motor vehicle. The RF signal also encodes whether the user wishes the doors to be locked or unlocked, the trunk to be unlatched or another function to be performed, as determined by which switch on the fob is pressed by the user. Encryption algorithms often are employed to make it extremely difficult for a thief to eavesdrop on the fob transmissions and learn the security codes.
A receiver mounted in the motor vehicle detects the transmission from the fob and decodes the RF signal to determine whether it is valid for that vehicle and which one of the various functions is to be performed. The receiver then activates the appropriate components to perform that function.
Conventional keyless entry systems require that the user activate the fob by pressing a switch in order to send a signal to the vehicle. If the user's arms are carrying packages or a child, it may not be convenient to activate the small fob located in a pocket or purse. Thus it is desirable to provide a passive keyless entry system that does not require fob activation by the user.
It is not uncommon for a family to have two or more vehicles each with a separate fob for remote access. This requires a person to either select the correct fob for the vehicle that is desired to be driven or to carry a fob for each vehicle. Thus it is advantageous to permit a single fob to access multiple vehicles. However, it is undesirable to have a single transmission from this fob unlock several vehicles when the user only wants access to one.